Measuring sensor

ABSTRACT

A measuring sensor, in particular for determining the oxygen content in exhaust gases of internal combustion engines, having a sensor element fixed in gastight fashion in a metal housing (14) and having a sealing flange (60) mounted on the housing (14) and resting on a sealing seat (76) embodied in an exhaust system (11). A union nut (80) is guided over onto the housing (14) and can be screwed into a thread (78) of an opening (70) provided in the exhaust system (11) and presses the sealing flange (60) against the sealing seat (76). The housing (14) has a housing part (12) on the side toward the gas to be measured and a further housing part (13) on the side toward the connection, and the sealing flange (60) is disposed on the housing part (13) on the side toward the connection and is shaped from the material of the housing part (13) on the side toward the connection.

PRIOR ART

The invention relates to a measuring sensor, in particular fordetermining the oxygen content of exhaust gases in internal combustionengines, having a sensor element fixed in a housing, a sealing flangemounted on the housing and resting on a sealing seat in an installedposition, and a fastening element which is guided over and onto thehousing and can be screwed into a threaded opening, with the fasteningelement pressing the sealing flange against the sealing seat.

From European Patent Application EP A1 624 791 (U.S. Pat. No.5,329,806), a gas sensor is known in which a sensor element is fixed ingastight fashion in a tubular metal housing. On its lower part thetubular housing has a radially outward-pointing lip that forms a sealingflange. The gas sensor is placed in an opening of an exhaust system,with the lip seated on a sealing seat embodied in the opening. A hollowscrew is guided over onto the housing and screwed into a thread disposedin the opening and thus connects the lip to the exhaust system in agastight fashion. A problematic aspect of this embodiment, however, isthat the pressing or upsetting of the relatively thin-walled material ofthe housing can cause microscopic cracks, which cause the housing toleak.

SUMMARY AND ADVANTAGES OF THE INVENTION

The above drawback of the known arrangements generally are overcomeaccording to the present invention by a measuring sensor, in particularfor determining the oxygen content in exhaust gases of internalcombustion engines, having a sensor element fixed in a housing, asealing flange mounted on the housing and resting on a sealing seat inan installed position, and a fastening element which is guided over andonto the housing and can be screwed into a threaded opening, with thefastening element pressing the sealing flange against the sealing seat,and wherein the housing has a housing part on the side toward the gas tobe measured and a housing part on the side toward the connection, andthat the sealing flange is disposed on the housing part on the sidetoward the connection.

The invention as defined above has the advantage over the prior art thatthe sealing flange is absolutely gastight. A two-piece housing with asealing flange disposed on the housing part on the side toward theconnection is not only simple to manufacture but can also be manipulatedeasily during assembly.

By means of other disclosed provisions advantageous further features ofand improvements to the measuring sensors according to the invention asdisclosed above are possible. Producing the sealing flange by theproduction process of rotary swaging has proved to be especiallyappropriate. It is also expedient to attach a connection piece to theexhaust pipe; this piece then forms a sealing seat for the sealingflange on its end face. By mounting a union nut on the sealing flangeand by its cooperation with a thread provided on the connection piece,the sealing flange is joined in gastight fashion to the connectionpiece.

BRIEF DESCRIPTION OF THE DRAWING

An exemplary embodiment of the invention is shown in the drawing anddescribed in further detail in the ensuing description. The sole drawingFigure is a longitudinal section through a gas sensor inserted into anexhaust pipe.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENT

A gas sensor 10, such as an electrochemical oxygen sensor, is insertedinto an exhaust pipe 11 and has a metal housing part 12 on the sidetoward the gas to be measured and a metal housing part 13 on the sidetoward the connection, which together form a housing 14. A planar sensorelement 16 having a portion 17 on the side toward the gas to be measuredand a portion 18 on the side toward the connection is fixed in thehousing 14 in gastight fashion.

The housing part 12 on the side toward the gas to be measured is a tubeelement, for instance open on both ends, with a cylindrical wall 21 onthe inside. On its end on the side toward the connection, the housingpart 12 on the side toward the gas to be measured has a portion 22, forinstance, of lesser outer diameter and lesser inside diameter. As aresult, an outer annular face 23 and an inner annular face 24 are formedon the tube element. The housing part 12 on the side toward the gas tobe measured also, for instance on its end on the side toward the gas tobe measured, has a cylindrical bush 34, which extends past the end onthe side toward the gas to be measured of the sensor element 16 andthereby forms an outer guard bush 36 for the portion 17 on the sidetoward the gas to be measured of the sensor element 16.

Disposed in the bush 34 is an inner guard bush 38, which surrounds theportion 17 on the side toward the gas to be measured of the sensorelement 16 with clearance and forms a measurement gas chamber 40 in itsinterior. The inner guard bush 38 has a bottom 42, in which a firstopening 43 is made, where gas can flow in and/or out. On the endopposite the bottom 42, the inner guard bush 38 is embodied with aflange 45, in which further openings 46 through which the gas can flowin and/or out are provided. However, it is also possible for the bush 34to be joined as a separate part to the inner guard bush 38 and for theresultant preassembled double guard bush then to be welded, e.g., by theweld 48 to the tube element.

In the housing part 12 on the side toward the gas to be measured, thereare a molded ceramic part 26 on the side toward the gas to be measured,a molded ceramic part 28 on the side toward the connection, and asealing element 30 between them. The molded ceramic parts 26 and 28comprise Al₂ O₃, for example, and have leadthroughs, not identified byreference numeral, for the sensor element 16. The sealing element 30comprises steatite, for example, and is inserted in a prepressed statein which it likewise has a leadthrough for the sensor element 16.

The fixation of the sensor element 16 in the housing part 12 on the sidetoward the gas to be measured is accomplished by inserting the moldedceramic part 28 on the side toward the connection, the sealing element30 in the pressed state, and the molded ceramic part 26 on the sidetoward the gas to be measured into the housing part 12 on the sidetoward the gas to be measured in succession. The molded ceramic part 28on the side toward the connection then rests on the inner annular face24. The leadthroughs for the sensor element, which are not identified byreference numerals, are located in alignment one above the other. Next,the sensor element 16 is thrust through the leadthrough, until itassumes its specified axial position. Then, on the side toward the gasto be measured, a contact pressure force is exerted on the moldedceramic part 26 on the side toward the gas to be measured with a maledie, the contact pressure force being dimensioned such that theprepressed sealing element 30 is crushed, causing its powderedcomponents to press against both the sensor element 16 and the innerwall 21. During the exertion of force on the molded ceramic part 26 onthe side toward the gas to be measured, a radially extending,inward-pointing indentation 32 on the end on the side toward the gas tobe measured of the molded ceramic part 26 on the side toward the gas tobe measured is made in the tube element. As a result, the molded ceramicpart 26 on the side toward the gas to be measured is held in thecompression position with respect to the sealing element 30.

The housing part 13 on the side toward the connection is embodiedcylindrically and has a tapering portion 52 with an opening 53. A metaljacket tube 55, for instance, is welded into the opening 53. Connectioncables 57 for the sensor element 16 are passed through the jacket tube55. The connection cables 57 are connected to contacting elements 49,which are contacted with connection contacts, not identified byreference numeral, on the portion 18 on the side toward the connectionof the sensor element 16. The contacting of the sensor element 16 can berealized for instance by clamping or by means of a materially joinedconnection. However, where the cable emerges through the opening 53 canalso be in the form of a temperature-resistant PTFE cable leadthrough.

On the end toward the sensor element, the housing part 13 on the sidetoward the connection has a radially encompassing sealing flange 60,which has an upper annular face 61 and a lower annular face 62. Thesealing flange 60, in the present exemplary embodiment, is formed fromthe material of the housing part 13 on the side toward the connection.The sealing flange 60 may be produced by various deforming processes.Rotary swaging has proved to be an especially suitable deforming processwith which a stable sealing flange 60 can be shaped from the material ofthe housing part 13 on the side toward the connection. However, as analternative, it is also conceivable for weld a ring onto the cylindricalhousing part. 13 on the side toward the connection, and this ring thenforms the sealing flange 60.

Once the sensor element 16 has been contacted with the contact elements59, the housing part 13 on the side toward the connection is mounted onthe portion 22 of the housing part 12 on the side toward the gas to bemeasured, with the outer annular face 23 of the housing part 12 on theside toward the gas to be measured acting as an axial stop. Next, thehousing part 13 on the side toward the connection is welded gastight tothe housing part 12 on the side toward the gas to be measured by meansof a radially encompassing weld seam 65.

An opening 70 is provided in the exhaust pipe 11, and into it acylindrical connection piece 72 is inserted by one end. The connectionpiece 72 is welded gastight to the exhaust pipe 11 by means of anencompassing weld seam 74. On its other end, the connection piece 72 hasa flat annular face 76, on which the lower annular face 62 of thesealing flange 60 rests. The annular face 76 thus forms a sealing seatfor the sealing flange 60. On its outer circumference, the connectionpiece 72 has a threaded portion 78.

A union nut 80 is guided over onto the housing part 13 on the sidetoward the connection by a female thread 81 and an inner annular face82. The female thread 81 is screwed onto the threaded portion 78 of theconnection piece 72, and the inner annular face 82 presses against theupper annular face 61 of the sealing flange 60. By tightening the unionnut 80, the lower annular face 62 of the sealing flange 60 is pressedfirmly against the annular face 76, forming the sealing seat, of theconnection piece 72. This creates a gastight fastening of the gas sensor10 in the exhaust pipe 11.

For fastening the gas sensor 10 in the exhaust pipe 11, other forms afastening means are also possible, however. An example is fastening bymeans of a hollow screw, which has a thread on its outer circumferencethat is screwed into a female thread disposed on the connection piece72, in which case the sealing seat for the sealing flange 60 must thenbe formed by an additional annular face in the interior of theconnection piece 72. It is also conceivable to place an adapter betweenthe connection piece 72 and the hollow screw; then the gas sensor 10 isseated with the sealing flange 60 on an annular face of the adapter, andthe adapter rests with further annular face on the annular face of theconnection piece 72.

We claim:
 1. A measuring sensor for determining an oxygen content inexhaust gases of internal combustion engines comprising:a sensor elementfixed in a housing, with the housing having a measuring-gas side housingpart and a connection-side housing part, with the connection-sidehousing part being fitted over a segment of the measuring-gas sidehousing part and at the fitted over segment being connected gas-tightwith the measuring-gas side housing part; a laterally extending sealingflange mounted on the connection-side housing part, with the sealingflange having an upper annular surface and a lower annular surface; agas tube for the gas to be measured, with the gas tube having anopening; a connection piece that encloses the opening in the gas tube ina gas-tight manner and has one end fastened to the tube at the openingand an opposite end provided with a thread, and with the measuring-gasside housing part extending into the connection piece and through theopening into the gas pipe; an additional annular surface formed on theconnecting piece and forming a sealing seat for the lower annularsurface of the sealing flange; and, a fastening element, that isseparate from the housing parts, extending over the connection-sidehousing part and engaging the thread to fasten the housing to theconnection piece, with the fastening element engaging and acting uponthe upper annular surface of the sealing flange to press the lowerannular surface of the sealing flange against the sealing seat of theconnection piece.
 2. The measuring sensor of claim 1, wherein thesealing flange is shaped from a material of the connection-side housingpart.
 3. The measuring sensor of claim 1 wherein the sealing flange wasproduced by rotary swaging.
 4. The measuring sensor of claim 2, whereinthe sealing flange was produced by rotary swaging.